Method of blending pyrotechnic mixtures

ABSTRACT

A method of blending pyrotechnic mixtures of the class which include an organic binder, fuel powder and oxidizer powder, comprising the dissolving of the binder in a first solvent in which it is substantially soluble and in which the fuel and oxidizer powders are substantially insoluble so as to form a binder solution, mixing the fuel and oxidizer powders into said binder solution, adding a second solvent to the product of the foregoing steps in which second solvent the binder, fuel powder and oxidizer powder are substantially insoluble in an amount sufficient to cause the precipitation of the major proportion of the binder, and then removing the solvents and drying the precipitate. This method produces a uniformly granulated product which needs no mechanical handling to secure the mixture or granulation, these properties being obtained in a wet environment devoid of the risk of explosion.

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Timer-mans atent 51 Mar. 2%, 11972 [54] METHQD 0F BLENDING PYROTECHNIC MIXTURES Hubert G. Timmermans, Beach, Calif.

[73] Assignee: ll-li-Shear Corporation, Torrance, Calif.

[22] Filed: June 23, 1969 [21] Appl. No.: 835,917

[72] Inventor: Manhatten Primary Examiner-Benjamin R. Padgett Assistant Examiner-Stephen J. Lechert, Jr. Attorney-Angus & Mon

[57] ABSTRACT A method of blending pyrotechnic mixtures of the class which include an organic binder, fuel powder and oxidizer powder, comprising the dissolving of the binder in a first solvent in which it is substantially soluble and in which the fuel and ox idizer powders are substantially insoluble so as to form a binder solution, mixing the fuel and oxidizer powders into said binder solution, adding a second solvent to the product of the foregoing steps in which second solvent. the W binder, fuel powder and oxidizer powder are substantially insoluble in an amount sufficient to cause the precipitation of the major proportion of the binder, and then removing the solvents and drying the precipitate. This method produces a uniformly granulated product which needs no mechanical handling to secure the mixture or granulation, these properties being obtained in a wet environment devoid of the risk of explosion.

8 Claims, No Drawings METHOD OF BLENDING PYROTECHNIC MIXTURES This invention relates to a method of blending pyrotechnic mixtures.

The standard method of blending pyrotechnic mixtures is a potentially dangerous and a time-consuming process. Mixtures of the class with which this invention is concerned include an organic binder, a fuel powder, and an oxidizer powder. These must be intimately mixed and the resulting product reduced to a desired particle size. It has been common practice to accomplish this in a doughy state condition which is semi-dry and which involves the risk of including dry portions which might be ignited by mechanical forces. Accordingly, such mixtures are generally made in only small batches and with extreme care.

It is an object of this invention to overcome the foregoing disadvantages, to produce an intimate mixture, and select a particle size entirely in a wet state in the presence of excess liquid whereby no mechanical forces need be exerted on dry or semi-dry materials. Accordingly, it is possible to compound this mixture in large batches without risk. For example, with presently known techniques it is rare to compound mixtures of more than about 100 grams at a time while with this technique mixing several pounds at a time involves even less risk.

The standard technique for blending pyrotechnic mixtures of the class concerned in this invention is to place all the materials in a ball mill or blender, wet them with a solution, and blend the product in the blender for a time which ranges between about 2 to about 16 hours.

When the mixture reaches a semi'dry doughy condition, it is granulated by pressing it through a US. standard sieve of appropriate size to create the desired particle size. This is done by pressing it through the sieve with a rubber policeman and/or a stiff brush. This granulation step can become very hazardous when a large batch is made, because part of the explosive mixture can dry up before the granulation is completed, and become very dangerous to handle. Furthermore, some of the material is lost in the blender and some of it is lost in the sieve. These steps are therefore not only expensive, but are hazardous and require later clean-up steps which themselves are hazardous. While other blending techniques are known, these others also require the batch size to be restricted, and still involve an element of risk. The instant method of blending pyrotechnic mixtures avoids the foregoing problems.

The present invention is concerned with the blending of pyrotechnic mixtures which utilize an organic binder in the nature of a fluoroelastomer, a preferred example of which is Viton B, together with a fuel powder and an oxidizer powder. Viton rubber is a linear copolymer of vinylidene fluoride and hexafluoro-propylene, containing about 65 percent fluorine. Viton-B is a kind of Viton rubber. While it forms no limitation on this invention, one example of a pyrotechnic mixture which can readily be manufactured in accordance with this invention is a mixture consisting of percent of Viton B, 49% of Zr, and 46% ofKClltL, the percentages being by weight.

The method is conducted in several steps, the first of which consists of dissolving the binder in a first solvent in which it is substantially soluble and in which the fuel and oxidizer powders are substantially insoluble so as to form a binder solution. When Viton B is utilized, the first solvent is acetone.

The next step is to mix the fuel and oxidizer powders into said binder solution. This is a blending technique, and the mixture is thoroughly stirred so as to form a condition as close to a stable suspension as possible. Usually, the granular size of the powders will be quite small, so as to tend to remain suspended in the binder solution.

The next step is to add a second solvent to the resulting l l l suspension, in which second solvent the binder, the fuel powder and the oxidizer powder are substantially insoluble. When Viton B is used the second solvent will be heptane. The second solvent will be added in an amount sufficient to cause the precipitation of the major proportion of the binder. This is a two-phase liquid system, the two solvents being substantially immiscible and neither being substantiallysoluble in the other. As the binder precipitates out of its solution, the fuel and oxidizer powders appear to adhere to the surfaces of the precipitate so that a uniform mixture is obtained. This uniform mixture is in a solid state and settles to the bottom of the container.

The particle size of the precipitate is a function of the temperature of the solution, and it will be noted that the faster the rate of precipitation the larger will be the particle sizes. This rate is inverse to temperature. Therefore, particle sizes may be decreased by increasing the temperature and vice versa. A minor amount of experimentation will determine the most suitable conditions for this precipitation process, and determine the particle size.

After the precipitate has settled, the solvents may be removed, preferably by decanting, and the precipitate is dried. There is no need to granulate it because it is already granular, and the use of sieves and the like is eliminated. Furthermore, no material is lost with this process because in the two-phase system it will be found that no important amount of the powders or of the binder will remain in solution in either of the solvents.

There thereby results a method of blending pyrotechnic mixtures which is conducted entirely in the liquid phase where there is no risk of explosion, and which produces from this wet operation a dry properly granulated material of suitable and predetermined granular size.

I claim:

1. The method of blending pyrotechnic mixtures which mixtures include an organic binder, and fuel and oxidizer powders, said method comprising:

a. dissolving the binder in a first solvent in which it is substantially soluble and in which the fuel and oxidizer powders are substantially insoluble so as to form a binder solution;

b. mixing the fuel and oxidizer powders into the binder solution;

c. adding a second solvent to the mixture of step b. in which second solvent the binder and the powders are substantially insoluble in an amount sufficient to cause the precipitation of the major proportion of the binder; thereby to provide in a liquid system a mixture of solid binder, fuel and oxidizer and d. removing the solvents and drying the solids from step c.

2. The method of claim 1 in which the first solvent is acetone and the second solvent is heptane.

3. The method of claim 2 in which the binder is a fluoroelastomer.

4. The method of claim 3 in which the fluoroelastomer is of vinylidene fluoride and hexafluoro-propylene, containing about 65 percent fluorine.

5. The method of claim 1 in which the two solvents are substantially immiscible with, and substantially insoluble in, one another.

6. The method of claim 5 in which the first solvent is acetone and the second solvent is heptane.

7. The method of claim 6 in which the binder is a fluoroelastomer.

8. The method of claim 7 in which the fluoroelastomer is a linear copolymer of vinylidene fluoride and hexafluoropropylene, containing about 65% fluorine.

Patent No, Dated March 28,

Hubert G. Timmermans Inventor s) It is certified that above-identified patent and that said Letters Patent as below:

In the "References Cite l/i364 should read "1/1964" Col. 2, line 49 before "and" insert a semi-colon (Claim 1, line 15) C01. 2, line 55 "is insert --a linear copolymer (claim 4, line 1) Signed and sealed this let day of October 1974.

(SEAL) Attest:

Ce MARSI'DXLL DANN McCOY M. GIBSON JR,

Commissioner of Patents Attesting Officer FORM PO-105O (10-69) USCOMMDC 5Q376-P69 9 U.S. GOVERNMENT PRIN'HNG OFFICE 8G9 0-366-334 v UNITED SEA' IES F TEM OFFICE CERTIFICATE 0F CGRRECTION Patent No. v 3,652,350 I Dated March 28, 1972 I Hubert G. Timer-mans It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below;

In the References Cited" 1/1064" should read "1/1964" Col. 2, line 49 I before "and" insert a semi-colon (Claim 1, linelS) Col. 2, line 55 after "is insert -a linear copolymer (claim 4, line 1) Signed and sealed this 1st day of October 1974.

(SEAL) Attest:

McCOY M. GIBSON JR. c. MARSHALL DANN Attesting Officer Ccmmissioner of Patents FORM po'wso uscoMM-Dc 60376-P69 9 v.5. GOVERNHENT HUN ING OFFICE: 19! 0-355-32 

2. The method of claim 1 in which the first solvent is acetone anD the second solvent is heptane.
 3. The method of claim 2 in which the binder is a fluoroelastomer.
 4. The method of claim 3 in which the fluoroelastomer is of vinylidene fluoride and hexafluoro-propylene, containing about 65 percent fluorine.
 5. The method of claim 1 in which the two solvents are substantially immiscible with, and substantially insoluble in, one another.
 6. The method of claim 5 in which the first solvent is acetone and the second solvent is heptane.
 7. The method of claim 6 in which the binder is a fluoroelastomer.
 8. The method of claim 7 in which the fluoroelastomer is a linear copolymer of vinylidene fluoride and hexafluoro-propylene, containing about 65% fluorine. 